Dynamic properties of horizontal and vertical eye movements in parkinsonian syndromes

We studied dynamic properties of horizontal, vertical, and oblique eye movements in 23 patients with the following parkinsonian syndromes: idiopathic parkinsonism (PD), multiple system atrophy (MSA), pure akinesia (PA), progressive supranuclear palsy (PSP), and cortical-basal ganglionic degeneration (CBGD). Compared with age-matched controls, only PSP patients showed slowing of saccades. Patients in all groups showed saccadic hypometria that was most marked vertically. The trajectories of saccades made to diagonal target jumps were deviated toward the horizontal plane, due to the vertical hypometria; this was most marked in PA and PSP groups. Saccade latency was only increased in the CBGD group. Sinusoidal smooth pursuit did not differentiate between controls and patients; however, with step-ramp stimuli, pursuit eye acceleration was impaired in all patient groups compared with controls. The vestibulo-ocular reflex, with or without visual enhancement, was similar in patients and controls. These findings indicate that (1) in parkinsonian syndromes apart from PSP, the saccade-generating brainstem burst neurons are probably spared, but the signals that they receive, specifying the size and direction of saccades, are flawed; and (2) measurements of the gain and trajectory of oblique saccades, and initiation of smooth pursuit, may aid in diagnosing these different types of parkinsonism.